1. Field of the Invention
The present invention relates to a thin-film magnetic head for magnetic recording which writes data to a magnetic recording medium and/or reads data from the medium, a head gimbal assembly (HGA) provided with the thin-film magnetic head, and a magnetic recording/reproducing apparatus provided with the HGA. Especially, the present invention relates to a thin-film magnetic head having an antistatic means for a protective coat of element ends.
2. Description of the Related Art
As magnetic recording/reproducing apparatuses, in particular magnetic disk drive apparatuses, increase in capacity and reduce in size, thin-film magnetic heads are required to have higher sensitivity and larger output. To respond to the requirement, a tunnel magnetoresistive (TMR) effect, which is expected to show extremely high resistance-change ratio, attracts attention, and actually thin-film magnetic heads having the TMR effect element as a read head element for reading data are being intensively developed.
The TMR effect element has a structure in which a TMR effect multilayer is sandwiched between two electrode layers. The TMR effect multilayer has a magnetization-pinned layer (pinned layer) in which the magnetization direction is fixed, a magnetization-free layer (free layer) in which the magnetization direction can change according to an applied magnetic field, and a tunnel barrier layer as an energy barrier in the tunneling effect which is sandwiched between the pinned layer and the free layer. Therefore, a sense current, which is applied during detecting magnetic field, flows in a direction perpendicular to the layer planes of the TMR effect multilayer as well as in the case of a current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) effect element.
One end surfaces of the two electrode layers and the TMR effect multilayer in the TMR effect element reach a head end surface on the air bearing surface (ABS) side of a slider substrate. Further, a protective coat, which is made of an insulating film such as a diamond-like carbon (DLC), is usually formed on the head end surface so as to cover the end surfaces of the electrode layers and TMR effect multilayer, and protects these end surfaces from wearing with the magnetic disk.
Conventionally, the above-mentioned head has a possibility that a noise occurs in read signals due to an electrostatic charge on the head. The noise is caused, for example, by a discharge between the magnetic medium such as a magnetic disk and the head. As a measure against the discharge, for example, Japanese Patent Publication No. 05-46941A describes a thin-film magnetic head that has a ground structure for preventing the discharge, formed of a non-magnetic conductive material. Further, in some cases, an ion milling process causes an electrostatic charge of the TMR effect element. As the measure against the electrostatic charge, for example, Japanese Patent Publication No. 2005-11409A describes a thin-film magnetic head in which the electrostatic charge is prevented by devising the formation order of the head elements. Furthermore, the contact of a magnetoresistive (MR) effect element with the magnetic disk might cause an electrostatic charge of the MR effect element, which has a possibility to bring a damage or breakdown of the MR effect element. As the measure against the electrostatic charge, for example, Japanese Patent Publication No. 06-243434A describes a technique providing a film with a predetermined electric resistivity on an opposed-to-medium surface of the head.
Further, though in the case of a giant magnetoresistive (GMR) effect element, Japanese Patent Publication No. 2001-250207A describes a technique in which a resistor is provided, for example, between upper and lower magnetic shields to prevent the destruction of the GMR effect element due to large currents flowing when an electrostatic breakdown of the element occurs. Furthermore, Japanese Patent Publication No. 2001-84543A describes a technique in which a bump connected with head elements is provided on one end surface of the slider substrate to avoid an electrostatic breakdown of the head element during deposition by using an electron-cyclotron-resonance chemical vapor deposition (ECR-CVD) method or during dry-etching, in the head manufacturing process.
However, there has been a conventional problem that a noise may occur, which is caused by a capacitor formed between the surface of the protective coat made of an insulating film such as a DLC and the end surfaces reaching the head end surface of the two electrode layers and the TMR effect multilayer. The capacitor may be generated by the voltage potential difference due to the electrostatic charge between the surface of the protective coat and the end surfaces of the two electrode layers and the TMR effect multilayer. The electrostatic charge may be generated by, for example, the friction with the magnetic recording medium during loading. It is significantly difficult to solve this noise problem even by using the above-described conventional art.
For example, the provision of the film with a predetermined electric resistivity on an opposed-to-medium surface of the head described in Japanese Patent Publication No. 06-243434A can avoid the formation of the capacitor. However, the film cannot be applied to the case with a TMR effect element because the film short-circuits the two electrode layers of the element.
As a further problem, the tunnel barrier layer of the TMR effect element is formed of an insulating material. Therefore, an electrostatic charge may be generated between the pinned layer and the free layer sandwiching the tunnel barrier layer during a period of not operating when a sense current does not flow. As a result, the electrostatic charge causes a voltage potential difference between the TMR effect element and the surface of the protective coat. In this case, when the end surface of the TMR effect element has a smear as a short-circuiting part such as polish traces or the tunnel barrier layer has pinholes, these parts act as a trap site to accumulate electric charges. And when a read operation starts and the sense current flows, an electric noise may be generated due to the non-uniform voltage application to the tunnel barrier layer. It is also significantly difficult to solve this electric noise problem even by using the above-described conventional art.
Further, the CPP-GMR effect element has end surfaces of the two electrode layers and the GMR effect multilayer, which reach the head end surface on the ABS side of the slider substrate, as well as the TMR effect element has. Therefore, the CPP-GMR effect element also has the above-described problem that the noise may occur, which is caused by the voltage potential difference due to the electrostatic charge between the end surface of the element and the surface of the protective coat. Therefore, it is also significantly difficult for a thin-film magnetic head with the CPP-GMR effect element to solve the noise problem by using the above-described conventional art.